Guy Edwardes / Cracked earth in dry riverbed, Landmannalaugar, Iceland.

Cyril Ruoso / Mute swan (Cygnus olor) feeding underwater, Burgundy, France, March.

Cyril Ruoso / Mute swan (Cygnus olor) feeding along riverbed, viewed underwater, Burgundy, France. November.

Cyril Ruoso / Mute swan (Cygnus olor) feeding along riverbed, viewed underwater, Burgundy, France. November.

Cyril Ruoso / Mute swan (Cygnus olor) feeding along riverbed, viewed underwater, Burgundy, France. November.

Franco Banfi / Aquatic plants growing on bottom of the main spring at Rio Sucuri, Bonito, Mato Grosso do Sul, Brazil

Franco Banfi,Franco Banfi / Piraputanga (Brycon hilarii) in the main spring Aqua?o Natural that goes in the Rio Bai?Bonita, Bonito, Mato Grosso do Sul, Brazil

Franco Banfi / Piraputanga (Brycon hilarii) reflecting on the water surface, Aqua?o Natural, Bonito, Mato Grosso do Sul, Brazil

Michel Roggo / Brown bear (Ursus arctos beringianus) fishing for Sockeye salmon in the Ozernaya River, Kamtchatka, Russia, August

Alex Mustard,Alex Mustard / A female (in front) and male Sockeye salmon (Oncorhynchus nerka) over eggs in their spawning river. Adams River, British Columbia, Canada, October.

Linda Pitkin / 2020VISION / White clawed crayfish (Austropotamobius pallipes) underwater on riverbed, showing defensive posture, River Leith, Cumbria, England, UK, September 2012. Did you know? White clawed crayfish can live fo...

Linda Pitkin / 2020VISION / White clawed crayfish (Austropotamobius pallipes) underwater on riverbed, River Leith, Cumbria, England, UK, September 2012.

Linda Pitkin / 2020VISION / Brown trout (Salmo trutta) fry on river bed, Cumbria, England, UK, September.

Michel Roggo / Grayling (Thymallus thymallus) on spawning ground. Lac de Fenetre, alpine lake, 2456 m above sea level, Canton of Valais, Switzerland, June.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration; males surrounding a female. Adams River, British Columbia, Canada, October.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration. Adams River, British Columbia, Canada, October.

Laurie Campbell / Brown trout (Salmo trutta) resting on river bed near the Aigas Field Studies Centre, Inverness-shire, Scotland, July

Graham Eaton / Underwater landscape within a mountain stream, showing water turbulence, Snowdonia NP, Gwynedd, Wales, UK, December

Graham Eaton / Underwater view of River Glaslyn rapids, Snowdonia NP, Gwynedd, Wales, UK, April

Graham Eaton / Under the ice scene of freshwater frozen lake. Llyn Dinas, Snowdonia, Wales, December 2010.

Todd Mintz / Sockeye salmon (Oncorhynchus nerka) split level view of salmon on river bed, annual spawning run, Adams River, British Columbia, Canada, October

Willem Kolvoort / Aquatic plants in River Black Drim, Albania, Eastern Europe, May

Orsolya Haarberg / Eurasian beaver (Castor fiber) swimming underwater, Telemark, Norway, June

Alex Mustard / A Florida manatee (Trichechus manatus latirostrus) head portrait in Three Sisters Spring. Crystal River, Florida, USA. February 2010

Alex Mustard / A group of Florida manatees (Trichechus manatus latirostrus) sleeping in the afternoon at Three Sisters Spring. Crystal River, Florida, USA. Manatees sleep on the bottom of the spring, floating up per...

Alex Mustard / Two Florida manatee (Trichechus manatus latirostrus) surfacing to breathe, in morning light. Three Sisters Spring, Crystal River, Florida. USA. January

Graham Eaton / An underwater view of a mountain stream showing internal reflections on the water surface, Snowdonia NP, Gwynedd, Wales, UK, December 2009.

Graham Eaton / Underwater view of River Glaslyn rapids, Beddgelert, Snowdonia NP, Wales, April 2010.

Michel Roggo / Chub fish (Leuciscus cephalus) and Mute swan (Cygnus color) swimming over, Rhine river, Schaffhausen, Switzerland. RUNNER-UP - Wildlife Photographer of the Year 2010.

Michel Roggo / Underwater landscape in Hongrin River with ice on the river bed and surface in winter. Fribourg, Gruy?, Switzerland, December

Vincent Grafhorst / Ostrich (Struthio camelus) chicks walking on Nossob Riverbed, Nossob River, Kgalagadi Transfrontier Park, Botswana

Vincent Grafhorst / Spotted Hyena (Crocuta crocuta) pregnant female walking in riverbed of the Nossob River, Kgalagadi Transfrontier Park, Nossob River, Botswana

Henley Spiers / Male Three-spined stickleback (Gasterosteus aculeatus) showing breeding colouration, guarding its eggs which are hidden underground in an aerated nest, River Otter, Devon, England, UK.

Henley Spiers / Male Three-spined stickleback (Gasterosteus aculeatus) showing breeding colouration, guarding its eggs which are hidden underground in an aerated nest, River Otter, Devon, England, UK.

Henley Spiers / Air bubbles erupting from sediment on the riverbed, River Otter, Devon, England, UK. April.

Henley Spiers / Male Three-spined stickleback (Gasterosteus aculeatus) showing breeding colouration, guarding its eggs which are hidden underground in an aerated nest, River Otter, Devon, England, UK.

Henley Spiers / Underwater view of a wetland created by the activity of beavers, River Otter, Devon, England, UK.

Henley Spiers / European bullhead (Cottus gobio) portrait, River Otter, Devon, England, UK.

Henley Spiers / Mayfly nymph (Ephemeroptera) on riverbed with light spectrum running over its body, River Otter, Devon, England, UK.